Several digital multimedia broadcasting systems including terrestrial wave DMB has recently just started being served in earnest. In preparation for the service, the development of portable terminals capable of receiving Digital Multimedia Broadcasting (DMB), as well as the broadcasting systems, is being developed.
Furthermore, a complex type terminal capable of receiving two kinds of services through one portable terminal is actively being developed in conjunction with the existing mobile phone system.
However, the frequency bands used in the DMBs are 174 to 216 MHz which is chiefly a low frequency band, such as UHF or VHF. Accordingly, there are several restrictions to the development of portable terminals.
The most significant restriction is a problem relating to the size of an antenna basically used in the portable terminal.
In general, the size of the antenna is increased with a used frequency being lowered. In order to fabricate an antenna for a UHF or VHF band, a length of several tens of cm is required. However, the antenna is not suitable to be used in the portable terminal. Accordingly, active research is being done on a reduction in the size of an antenna for the portable terminal.
The existing whip antenna or helical antenna of a monopole type is configured to protrude externally from the portable terminal, and thus the use of the antenna of this type is decreased. There is a lot of interest in a built-in type antenna which is fully put in the portable terminal and not externally protruded, and various portable terminals using the built-in type antenna are emerging.
One of the built-in type antennas is a Printed Circuit Board Antenna (hereinafter referred to as a ‘PCB antenna’).
The PCB antenna is characterized in that the shape of the antenna is chiefly flat. The PCB antenna can be easily implemented with a low cost and can solve problems in the process, as compared with a coil type antenna.
FIG. 1A is a plan view of a PCB antenna which is a conventional built-in type antenna and, FIG. 1B is a cross-sectional view taken along line I-I′ of the plan view.
Referring to FIGS. 1A and 1B, the existing PCB antenna includes a PCB 10 having the components of a portable terminal mounted thereon and an antenna pattern 20 serving as a radiation substance patterned on the PCB 10 in a specific form. In general, a material chiefly used in the PCB is FR4, and the antenna pattern is printed using copper (Cu).
However, the PCB antenna (that is, the built-in type antenna) shown in FIGS. 1A and 1B also does not deviate from a correlation between the frequency and the size of the antenna, and thus the existing built-in type antenna has a very large size. In view of a trend toward a reduction in the size of and an increase in the functions of a current portable terminal, the built-in type antenna is also becoming a major factor to restrict a reduction in the size of the portable terminal.
In particular, a portable terminal for DMB operates in a low frequency band of 174 to 216 MHz, such as UHF or VHF, and has lots of difficulties in using the existing PCB antenna, such as that shown in FIGS. 1A and 1B. Accordingly, there is an urgent need for an antenna having a size more and more reduced
In order to solve the problems, a technique for constructing a substrate using high dielectric substances and forming a radiation pattern on the substrate has been developed and used. However, in the case where an antenna is implemented using high dielectric substances, a reduction in the size of the antenna may be achieved, but a disadvantage in that the gain and bandwidth of the antenna are decreased is inevitable.
The antenna using high dielectric substances as described above is not suitable for several DMB systems, including terrestrial wave DMB, which require a wide bandwidth and a high gain. Accordingly, there is a need for the development of a method of reducing the size of an antenna and satisfying a wide bandwidth and a high gain.